1. Field of the Invention
The present invention relates to a technology for backing up data stored in a primary storage into a secondary storage.
2. Description of the Related Art
A storage system that includes a primary storage (redundant arrays of inexpensive disk (RAID), etc.) and a secondary storage (a tape device, etc.) has a function of copying data to the second storage when the data has not been updated for a specified time period in the primary storage. For example, Japanese Patent Application Laid-open No. 2001-100931 discloses a storage system having such a function.
The conventional storage system records the time of the data update per specific data unit (MRB <Migration/Recall Block>) to check elapsed time since data was stored in the primary storage. The storage system performs a synchronization process (process of copying data from the primary storage to the secondary storage) based on the MRB.
Besides, a storage system with global file system (GFS) environment has a function of managing a plurality of logical unit numbers (LUN) as one LUN in the primary storage that can be seen from the host computer to reduce the burden on the host computer or the like.
FIG. 7 is a schematic for explaining functions of a conventional storage system. The conventional storage system with the GFS environment manages virtual logical units (VLUs) VLU 0 to 4 as one LUN. Data are updated for the LUN in order while the VLUs are switched in a specific range. In the example of FIG. 7, data update time is the oldest in MRB (1), and is newer in order of MRB (2), MRB (3), and MRB (4).
In the conventional storage system, tape devices are assigned to the VLUs, respectively, and therefore, the synchronization process is performed while the tape devices are switched each time the VLUs are switched. For example, in FIG. 7, VLU 0 switches to VLU 1 when the subject of the synchronization process switches from MRB (1) to MRB (2). Accordingly, the synchronization process is performed by switching a tape device corresponding to VLU 0 to a tape device corresponding to VLU 1.
In the conventional storage system, however, the tape devices are assigned to the VLU, respectively, and switching of the tape devices frequently occurs in the synchronization process. As a result, performance of the secondary storage is deteriorated and its life span is reduced.